Efficiency doesn't really matter if the energy is "free", as long as it can scale to produce reasonable quantities. If it could produce a liquid fuel for road transport that would be even better, since it could be distributed via existing networks.

The challenge for road networks is one of scale. Jet fuel is between 12% and 14% of global fuel consumption, and there is no feasible prospect of battery- or hydrogen-powered aircraft any time soon. They must use a hydrocarbon-based fuel for the foreseeable.

When you factor in the efficiency loss of combustion vs electric motors, from a whole-system perspective pure electric vehicles are best, so if you're building a boatload of new generation capacity to meet the needs of an evolving fleet you focus on EVs were you can. Liquid fuels (whether syngas or H2) should generally be reserved for the areas we know we're going to need them - aircraft, steel, fertiliser, construction and so on - rather than the domestic road networks.

We also shouldn't forget that while this would be carbon-neutral, burning hydrocarbons is responsible for tens of thousands of direct and indirect deaths due to all the other shite that's spat out the back of the car in the process.

A lot of the crap blown out of the exhaust is the result of the hoops they have to jump through to meet mandatory CO2 levels. If those were relaxed, due to the CO2 being recycled, the manufacturers would have more freedom to clean up their engines.

No, you focus on carbon neutral and zero carbon. EVs are just one path, and you can't ignore the global fleet of combustion engine vehicles that most people cannot afford to replace.

If you want global anarchy, just tell the billions of car owners, millions of businesses, they can no longer run their car/van/truck unless they switch to EV.

Plus why scrap a perfectly good vehicle just because it's not an EV. That's hardly ecologically sound.

How many people drive a car that's more than 25 years old? And how many of those do it because they can't afford anything else? (My experience is that cars get kinda expensive to maintain sometime before that age.)

The plan for the combustion fleet isn't to ban them from the roads, but simply to let them wear out.. What's important is that we stop making new ones.

...there is no feasible prospect of battery- or hydrogen-powered aircraft any time soon...

Actually for short haul flights electric propulsion does work but for long haul, not a chance.

85% of flights are short haul.

Plainly "Short haul" covers a wide range of flights even if only half are short enough to be electrified that's a significant proportion of flights.

Once suitable craft are produced all sub 100km flights, city to city or island hoppers can and should be electric.

It makes no difference. Greens are opposed to personal transport, not the emissions.

The emissions are a perfect cover, but they've already revealed that they are opposed to electric cars because of the dust given off by their brakes and tyres.

The Greens, at least in the UK, despite their name do not speak for anyone but themselves. We'd all be much better off if they'd stuck to their original name of the People Party, reflecting their reality not as environmentalists but a party run by committee of committees, committing to whatever nonsense those committees agree.

This also goes a long way to explaining why they have little electoral success here, in stark comparison to the rest of Europe.

Even if the energy is "free", the maintenance and labour costs will not be. So more process efficiency is still better ... as long as any increased costs associated with that efficiency gain are small enough.

Global-scale 20% efficiency conversion of solar power and air to Kerosene almost seems too good to be true. That's a similar level of efficiency as modern photovoltaic panels, but outputting a temperature-stable, energy-dense, power-dense, easy-to-handle fuel that can be burned in every gas turbine that already exists for no climate impact.

What's the catch?

Jet engines have an efficiency (at best) of about 40%

Car engines are similar.

There's are likely good use cases (yes jets) but won't be cheap for a long while.

The 20% is also the optimistic "please fund us more" number. Going from 4% will be a long path.

Also Bain & Co, a charming bunch.

https://www.bbc.co.uk/news/business-62408116

It doesn't scale. The article seems quiet on how much fuel can be generated per square metre of infrastructure, but it is probably not large and jets are quite thirsty.

Given a large area that you are willing to cover in solar something, you get several times better bang for your square metre if you just generate electricity.

Edit: I see that Twanky has used some napkins in a comment below. Ignore me and scroll down now.

Carbon neutral jet fuel is not a new concept. This development is just another chemical process for making it. Siemens and others have been working on it for some time.

In March 2021 Rolls Royce flew an Airbus A350 on 100% synthetic fuel https://www.theguardian.com/business/2021/jun/17/rolls-royces-jet-engines-to-run-on-synthetic-fuels-as-part-of-net-zero-plans

The big difference here is that existing syngas projects - including the British Airways and Rolls Royce demonstrators - are using biological matter as feedstock. This is either ambiguously described as "waste products" (e.g. cooking oil), in which case we have no hope of ever scaling to global needs or is derived directly from US-subsidised bio-ethanol, and carries a large cost in terms of land, water, fertiliser use, food price pressures and carbon impact.

Producing fuel straight from air in a cost-effective manner would be a game changer.

This process would also require land. Anything harvesting energy from sunlight uses the land on which that sunlight falls. If a process produces something from waste products (why do you use scare quotes?) then the land has already been used in whatever process it was wasted from. You also need to consider how the waste might otherwise have been disposed of; waste organic matter is apt to give rise to methane if simply buried.

Ideally we'd use the shittiest, least-otherwise-useful land on Earth for it.

There's plenty of land that has lots of sunlight but isn't suitable for agriculture.

They've used quotes because the "waste products" are either not really waste (there's plenty of uses for used cooking oil already), and to do it at the scale required to replace all aviation fuel, there's not enough "waste"to do it, so instead of using "waste", we'd be growing things specifically for use in this, and then they aren't waste at all. Not scare quotes, but noting that they think its a euphemism.

If you can do that for jet fuel we may as well run cars on the stuff, and forget batteries.

This was the plan to heat a collector to drive a reversible chemical reaction. The heat is now stored in a new gas mixture which does not need insulated pipes to carry it. At the store it would dump this into a huge mound of aerosol cans will with more-or-less common salt.

Everything was done to make the project scale up as the USN realised their energy usage could be measured in Quads*

The attrive feature about solar thermal is it acts as a black body, absorbine sunlight at any wavelength. There is no effective "Band gap" where verything with longer wavelength just heats the PV cell, and everything with short wavelenght gives the elctron a bit more energy (making them get to the cathode faster? I'm not sure if that translate into actual greater poweer output)

This also starts to close the cycle of CO2 emissions.

Sadly given that most of the GHG's have lifetimes ranging from decades to millenia (AFAIK only water vapor++ and tropospheric ozone are on the order of days or weeks) and GW potentials 1000x of times that of CO2 this will not stop the impending extinction of the human race. :-(

*1 quad= 172.45 million barrels of oil.

++ Water vapor is #1 and has a lifetime of 8-9 days. IOW if you surpress most evaporation to the atmospheree you could start to see improvement within 2 weeks. All you have to do is surpress (or drastically reduce) all evaporation of the worlds oceans, rivers and reservoirs (primarily the oceans, given the are 70% of the worlds surface area). How you do that is left as an exercise for the reader. May I suggest "ping pong balls."

I worked as a petrochem scientist for an oil refinery for 22 years Syngas is nothing new, it's been used for many decades, to for synthesis of various products in the refinery.

Yes, that's what makes this so interesting. Syngas chemistry is well understood so having large amounts of very cheap renewable syngas could be a game changer.

At 15kW they hope to be able to produce Kerosene at 20% efficiency.

Combustion energy of Kerosene is about 36MJ/l

So they need 36*5 = 180 MJ = 50 kWh to produce 1 litre of Kerosene.

For 15kW they focus solar energy onto a 16 inch aperture (square?) and average 2,500 solar equivalents. So their collecting reflectors are 16*16*2500 = 640,000 sq inch or 413m2.

To get 50kW they need 1,376m2 of reflectors

1,376m2 of reflectors should produce Kerosene at 1 l/h

A 747 jet burns kerosene at about about 136,000 l/h

To get 136,000 l/h they need about 187km2 of reflectors.

187km2 of reflectors to keep one 747 fuelled. Assuming the jet only flies the same number of hours the converter can run each day. Remember, this is at the suggested 20% efficiency - they've so far only got 4%

Yes, jet fuel is a poor example of when to use this. Combine that with the high temperature required and it limits where you can do it. For example, if you need water from the atmosphere you can't do this in the desert.

Other processes already exist at scale, like the [1]Sunfire one , but more work is required as we still need to reduce the temperatures required for the reduction.

The low hanging fruit is something that can be driven by wind power so it can run at night and store fuel locally in closed loop energy systems in areas where energy is required: anything off grid reduces peak load and, thus, how much capacity needs provisioning. And, if we can cover our domestic and industrial energy requirements like this in the winter, then in the summer we can consider other uses and long term sequestration.

I skimmed an [2]abstract by the Max Planck Institute that shows there is potential for improvement. We need to do more research on this and things like methanol fuel cells but, thus far, industry is holding out for bigger subsidies for the hydrogen white elephant.

[1] https://www.sunfire.de/en/syngas

[2] https://www.mpie.de/3174832/Electrochemical-CO2-reduction

how many suns would we need to meet the global need?

Kerosene is about 45 MJ/kg. At 15 kW and (hoped for) 20% efficiency they can optimally create one kilogram in 15000 seconds (just over 4 hours).

An A320 burns about 2500 kg/h kerosene. For one hour of flight it takes 10416 hours to produce the fuel. To put it all in perspective... you need to scale up with four order of magnitude just to support one plane.

There are, give or take, about 10000 planes in the air at any given time, some smaller, some larger. To support all planes you need to scale up with eight orders of magnitude . To make it worse; you need space for the mirrors. With the sun at about a kiloWatt per square meter and a scale of 15 times 10 8 , you will need 1500 km 2 constantly in the sun. Or, effectively, for the mirrors alone, you need four times the area around the globe to cover daylight and at least double that to mitigate clouds, accounting to about 12000 km 2 . Then you still need to place all the syngas installations and other infrastructure in place.

We are now talking the size of countries here, just to support our flying addiction.

(Darn, ninja'ed by Twanky)

It is not very popular to say, but all of the world could be powered by a 400 by 400km square of solar panel in the Sahara desert.

David MacKay wrote a book that showed how "easy" that is "Sustainable energy without the hot air"

Forbes had an article about it in 2016: We Could Power The Entire World By Harnessing Solar Energy From 1% Of The Sahara

From the Forbes article:

The total world energy usage (coal+oil+hydroelectric+nuclear+renewable) in 2015 was 13,000 Million Ton Oil Equivalent (13,000 MTOE) - see World Energy Consumption & Stats. This translates to 17.3 Terawatts continuous power during the year.

Now, if we cover an area of the Earth 335 kilometers by 335 kilometers with solar panels, even with moderate efficiencies achievable easily today, it will provide more than 17,4 TW power. This area is 43,000 square miles. The Great Saharan Desert in Africa is 3.6 million square miles and is prime for solar power (more than twelve hours per day). That means 1.2% of the Sahara desert is sufficient to cover all of the energy needs of the world in solar energy. There is no way coal, oil, wind, geothermal or nuclear can compete with this. The cost of the project will be about five trillion dollars, one time cost at today's prices without any economy of scale savings. That is less than the bail out cost of banks by Obama in the last recession.

Fine, as soon as we have that World Government and have abolished all terrorism and internal security threats. Until then, I can see a problem with have the world's energy supply located in one place with the mother-of-all-wires leading out to the rest of the planet.

Sure, in practice you'd need to have at least 12 hours of energy storage capacity all over the planet just to smooth out the diurnal variation in output from your panels and so in practice you'd probably put similar arrays in the middle of Australia and similar places, but there are plenty of countries that don't have "similar places" and they'd be 100% dependent on the reliability of supply from their sunnier neighbours.

On the other hand, you are quite correct to point out that how we currently power our civilisation is pretty idiotic. A commenter in another thread on this site noted yesterday that the supposedly extortionate price of nuclear power at the UK's proposed/under-construction/dither-for-decades next reactor is less than half of what we are now paying as a result of our "dash for gas" in the late '90s. (Hey, kids, can you believe that your parents actually did a dash for gas in the late 90s, about 20 years after "the Greenhouse Effect" entered the popular consciousness as a thing? It's because we closed down our nuclear program in the 80s and replaced it with ... nothing at all ... and then realised 10 years later than we were about to decommission most of our generating capacity.)

The researchers manage to be quite honest in describing their achievement, but at the same time they do an amazing job hyping their research.

Did you catch that they use an area of about 50 nanoWales (2 Tennis courts, or ~1080 square meter) to make a few drops of jet fuel per hour? And they never mention how much energy went into the pumps, valves and motors required to run the whole set-up, so it is not clear that the set-up creates more energy than it consumes.

This is the current reality of our energy transition -- a lot of hyped achievements that are only realistic when you pay no attention to the man behind the curtain (who is burning that cheap hydrocarbon energy to fuel you pipe dreams).

As a counterpoint, how many important scientific achievements started out by offering the best possible results that the technology could offer? Hyperbole aside, this seems like an interesting starting point and there may well be something of value to come from it.

on a tower-mounted solar reactor or is that a Solex reactor?

At least you get a powerful Laser for free with the Solex.